Punching tool for forming a cross-recess of a screw

ABSTRACT

In a cross-recessed screw forming punching tool having four ridges substantially orthogonally intersected, each ridge is circumferentially inclined at a predetermined angle to a respective radial main center axis.

United States Patent [1 1 Uozumi 1 Jan.7, 1975 1 PUNCHING TOOL FOR FORMING A CROSS-RECESS OF A SCREW [76] inventor: lwao Uozumi, 17-11, 7-ch0me,

Ebara, Shinagawa-ku, Tokyo, Japan [22] Filed: June 21, 1973 [21] App1.N0.:372,020

[301 Foreign Application Priority Data June 21, 1972 Japan .1 47-72639 [52] US. Cl. 10/7 [51] Int. Cl. B23g 9/00 [58] Field 01 Search 10/3, 5, 7, 26; 85/45 [56] References Cited UNITED STATES PATENTS 3,108,623 10/1963 Muenchinger 10/7 Muenchinger 10/7 Muenchinger 10/7 Primary ExaminerC. W. Lanham Assistant Examiner-E. M. Combs Attorney, Agent, or FirmFlynn & Frishauf [57] ABSTRACT In a cross-recessed screw forming punching tool having four ridges substantially orthogonally intersected, each ridge is circumferentially inclined at a predetermined angle to a respective radial main center axis.

2 Claims, 7 Drawing Figures g 29b 30b Patented Jan. 7, 1975 3 Sheetsheet 1 PRIOR ART) 3 Shoots-Sheet 2 PUNCHING TOOL FOR FORMING A CROSS-RECESS OF A SCREW BACKGROUND OF THE INVENTION This invention relates to a punching tool for forming a cross-recess of a screw.

A conventional cross-recessed screw has orthogonally intersected four grooves symmetrical to center axis of a screw, and it is turned tight by a screw driver having a corresponding outer shape. FIG. I shows the manner in which a +-shaped screw driver 12 is inserted in the corresponding cross-recess ll of the head of the screw driver. As will be evident from FIG. 1, when the driver is engaged with the corresponding crossrecess of a screw, a predetermined amount of clearance 13 (for example, 0.03 mm when the maximum diameter of the cross-recess is 4 5 mm) is actually created as a whole. For this reason the outer face of the driver is un-uniformly engaged with the corresponding inner wall surface of the recess. It is considered, however, that the screw is usually engaged with the bottoms of the four ridges 14 of the driver. In this case, the angular portion 16 of the cross-recess of the screw is radially urged by the bottom of each ridge. However, the angular portion has no resiliency in a radial direction and no sufficient engaging force is obtained between the driver 12 and the head 10 of the screw. Furthermore, the screw is liable to be drop down from the driver due to its own weight. When the driver is forcibly pressed into the cross-recess of the screw, any damage is made to the surface of the cross-recess of the screw.

When the screw is tightened or turned by the driver, the driver is liable to be idly turned due to the clearance, in a tightening direction, in the cross-recess as indicated by an arrow in FIG. 1. As a result, the ridge 14 of the driver is partly and un-uniformly engaged with the inner surface of the cross-recess of the screw. Thus, the tightening of a screw is not sufficiently and effectively made and damage to the cross-recess of the screw is made with the attendant disadvantage. This phenomenon also occurs during the removal of the screw.

SUMMARY OF THE INVENTION An object of this invention is to provide an improved punching tool for forming a cross recessed screw suitably engageable with the conventional driver and capable of being effectively turnable through the use of the driver.

A punching tool according to this invention has four ridges circumferentially inclined at a predetermined angle to the orthogonally intersected radial center axes.

With the embodiment according to this invention said angle is 3-6.

When the conventional driveris inserted into the cross-recess of a screw formed by the punching tool according to this invention, each ridge of the driver is resiliently engaged, at two locations nearer to the bottoms of the ridge, with the inner surface of each groove of a cross-recessed screw. Viewed from the driver as a whole, the driver is engaged, in eight locations, with the cross-recess of the screw and an urging force is directed in a circumferential direction to cause the driver to be resiliently engaged with the cross-recess of the screw, thus preventing a drop down of the screw from the driver due to the own weight. During the turning of the driver, that surface of the ridge situated on the right side is engaged with all the corresponding surface of the cross-recess of the screw. As a result, an effective tightening of the screw is obtained and any damage is hardly made to the corresponding surface of the crossrecess of the screw.Even when the screw is loosened, that surface of the ridge situated in the left side is, likewise, fully engaged with the associated surface of the cross-recessed screw.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a cross sectional view, partly showing the manner in which a driver is inserted into the converttional cross-recess of a screw;

FIG. 2 is a plan view partly showing one embodiment of a punching tool according to this invention;

FIG. 3 is a side view of the punching tool of FIG. 2 as reduced to a small scale;

FIG. 4 is a plan view, showing the cross-recess of a screw formed by the punching tool according to this invention;

FIG. 5 is a cross sectional view of a conventional driver;

FIG. 6 is a cross sectional view, partly showing the manner in which a conventional driver is inserted into the cross-recess of the screw formed by the punching tool according to this invention; and

FIG. 7 is a view similar to that of FIG. 6, partly showing the manner in which a driver is threadably engaged with the cross-recessed screw.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS. 2 and 3 conjointly, a punching tool according to this invention is provided with a holding member 20 and a punching body 21 fixed to the holding member. The punching body 21 is substantially in the conical shape and has an axial center axis 22-22 passing through a center point 0 of the holding body and holding member. The holding member has four ridges 23 substantially +-shaped in cross section. For convenience of explanation, the respective ridges are identified with suffixes a, b, c and d added. The ridges 23 project radially outwardly along the main radial axes 24-24 and 25-25 which are orthogonally intersected at the center point 0. The punching body 21 has four reference points 28 on auxiliary center axes 26-26 and 27-27 where the respective axes are intersected at an angle of 45 to the main center axes. A spacing B between the oppositely facing reference points 28 situated on the center line 26-26 or 27-27 can be determined according to an industrial standard of a punch and thus a cross-recessed screw. Likewise, an outermost peripheral diameter M of the ridges, as well as a spacing D defined between curved inner bottom portions of the adjacent ridges, is determined according to the industrial standard. The paired reference lines defined by the spacing D are spaced an equal amount from the respective auxiliary line.

There will now be explained the outer configuration of the base surface of the punching body 21 by reference to FIG. 2.

A left edge portion 29 of any ridge, for example 230, is inclined counter-clockwise at an angle of E to the main center axis 24-24 and is on the line where the reference point 28a is situated. The angle E is preferably 3-6. With this embodiment this angle is 4. The outer terminal end 30a of the left edge portion 29a is situated on an imaginary circle having a diameter M including the center axis 0. The inner terminal end 31a is located on a line determining the dimension D.

The right edge portion 32a of the ridge 23a is on the line inclined counter-clockwise at an angle of F (substantially the same as the angle E) to the main center axis 2424. This line passes through a point 33b nearer to the center line than the reference point 28b.

This arrangement causes the vicinity of the base of each groove (to be formed by each ridge of the punching tool) of a screw to be narrower to permit the inner wall of the groove to suitably engage with a screwdriver. To explain the dimension of the right edge portion 32a geometrically, an imaginary line 34a passing through the reference point 28b is described in a manner to be inclined at an angle of G to the center axis 24-24. Then, a main line passing through a point 35a intersected between the line 34a and the circle having a diameter M is described in a manner to be inclined at an angle of F to the center axis. The right edge portion 32a is on the main line, and the point 33b falls on a line intersected between the main line and a line made between the reference points 28a and 28b. In an attempt to obtain a standard angle (92? in this embodiment) between the outer terminal end 30 of the left edge portion and the outer terminal end 35 of right edge portion of the adjacent ridges, an angle G is determined to be 6.

The inner terminal end 36a of the right edge portion 32a is situated, like the inner terminal end 31 of the left edge portion, on the line determining the spacing D.

As mentioned above, the angle E can be selected, like the angle F substantially the same as the angle F, to be 3-6. The angle G may be suitably selected so that an angle 6 is obtained according to the angles E and F.

The adjacent inner terminal ends 31 and 36, for example, the inner terminal end 31a of the left edge portion 29a of the ridge 23a and the internal terminal end 36d'of the left edge portion 32d of the ridge 23d fall on a circle having an arc R with a point 37a as a center. The point 37a is located on a center line 60 equidistantly spaced from the inner terminal ends 31a and 36d. The value of the radius R is suitably selected to permit the inner portion nearer to the points 31 and 36 in the cross-recess of a screw to suitably engage with the screw driver upon insertion of the screw driver into the cross-recessed screw, as will be later described. With the embodiment, the point 37a falls on a point intersected between the center line 60 and the line 61 passing through the point 33a and inclined at an angle of 20 to the center axis 27-27. The radius R is equal to the distance between the point 37a and the point 31a.

Turning to FIG. 3, the punching body 21 whose base portion is so constructed is converged at'an angle of or towards the point 0, present on the center axis 22-22.

In FIG. 4 there is shown a cross-recess 41 of a screw head 40 formed by the punching tool according to this invention. As will be evident from this Figure, the

cross-recess so formed is substantially the same as the punching body 21, except that it is inclined in a clockwise direction, and has four grooves 42 corresponding to respective ridges 23 of the punching body.

A conventional screw driver 12 as shown in FIG. 5 has four ridges 14 whose radial center axes 44-44 and 45-45 are orthogonally intersected to obtain a line symmetry. A spacing B, between reference points 47 of the screw driver and a spacing D between the inner terminal ends 48 and 49 of the edges of the screw driver are equal to the dimensions B and D of the punching body 21 as shown in FIG. 2 and thus the dimensions B and D of the screw as shown in FIG. 4. The angle 0 is also equal to the angle 0. Adjacent inner peripheral ends 48 and 49 are, as is well known in the art, not on the arc, but on an angular edge portion 50.

FIG. 6 shows the manner in which the screw driver 12 as shown in FIG. 5 is axially inserted into the crossrecess 41 as shown in FIG. 4. Since, as mentioned above, each groove 42 of the cross-recessed screw is inclined clockwise, the right edge portion 51 of each ridge 14 of the screw driver is, on continuous insertion into the cross-recessed screw, abutted against the right inner wall 52 of each groove 42. At this time, the abutted portion x of the right edge portion of each ridge is situated on that portion of the angular edge 50 nearer to the inner terminal end 48 of the edge 51. And the abutted portion X of the right inner wall 52 of the groove is situated on that portion of a merging inner wall 54 closer to the inner terminal end 53 of the inner wall 52. The screw head portion 55 in the vicinity of the merging inner wall 54 of the cross-recessed screw has an appreciable resiliency against a peripheral force. When the screw driver is further inserted, each ridge 14 is forced in a counter-clockwise direction by the screw head portion. For this reason, the left edge portion 56 of the ridge is abutted against the inner wall portion Y closer to the inner terminal end 58 of the inner wall 57. The portion Y is substantially symmetrical to the abutted portion X. As a result, a clearance is created between the right edge portion 51 and the right inner wall 52 and between the left edge portion 56 and the left inner wall 57. The former clearance defines a small angle of H and the latter clearance defines a small angle of I substantially the same as the small angle of H. Thus, the screw driver engages with eight locations (x, y), not with four locations as is the case of the prior art. A resilient urging force from the inner wall of the screw recess is applied substantially in a circumferential direction to the outer wall of the screw driver, so that a resilient and uniform urging engagement of the driver with the screw head is obtained at the respective contact points. In this way, a positive engagement of the crossrecessed screw with the screw driver assures no drop down of the screw due to its own weight and entails no damage to the inner wall of the screw.

As shown in FIG. 7, when the screw driver is turned in the clockwise direction, the ridge 14 of the screw driver is forcefully urged on the merging inner wall 54 of the cross-recess of the screw. The merging portion has, as mentioned above, an appreciable resilience against the force urging in the circumference direction, and is urgingly compressed in a clockwise direction by the ridge of the screw driver. As a result, the right edge portion 51 of the ridge is engaged all over the right inner wall 52 of the cross-recessed screw groove. At this time the left edge portion 56 is disengaged from the left inner wall 57, leaving a relatively larger clearance 59 therebetween. Thus, the screw is effectively screwthreaded and damage to the inner wall of the screw is suitably prevented.

The screw driver 12 is, upon removal of the screw, turned in the counter-clockwise direction. Even in this case, the left edge portion 56 of the ridge 14 is likewise contacted all over the left inner wall 57 of the groove 42 of the cross-recessed screw.

As mentioned above, the cross-recess formed by a punching tool according to this invention can be engaged, at eight locations, with a screw driver under a resilient and uniform force. The screw driver, upon continued turning, is abutted against all over the inner wall on the one side of each groove. The engaging force obtained at eight locations can be varied by suitably selecting any inclination angles E, F of the ridge of the punching tool.

What is claimed is:

1. In a cross-recessed screw forming punching tool provided with a cone-shaped punching body having four ridges, said ridges radially projecting along main radial axes orthogonally intersecting with each other at the center point of the punching body, the lateral side edges of the ridges having a predetermined positional relationship relative to four reference points which are spaced from adjacent reference points by a first standard spacing and fall on auxiliary radial axes, wherein:

said axiliary axes pass through said center point and intersect the main axes at an angle of 45;

the radially inner ends of said lateral side edges terminate at pairs of reference lines parallel to and spaced by a second standard spacing from the auxiliary radial axes;

the inner end of the one lateral side edge of each ridge is connected by an intersecting portion with that of the other lateral side edge of the adjacent ridge;

one of the lateral side edges of each ridge extends along a line which diverges at an angle 36 from an associated main radial axis and passes through an associated reference point;

the other lateral side edge of said ridge extends along a line which converges toward the main axis at the same angle as said one lateral side edge and passes through a point nearer to the main axis than an associated reference point; and

said intersecting portion is formed in a curved concave shape.

2. A cross-recessed screw forming punching tool according to claim 1, wherein said intersection portion is shaped in the form of an arc having its center point equidistantly spaced from the inner ends of the lateral side edges of the adjacent ridges.

* l l l 

1. In a cross-recessed screw forming punching tool provided with a cone-shaped punching body having four ridges, said ridges radially projecting along main radial axes orthogonally intersecting with each other at the center point of the punching body, the lateral side edges of the ridges having a predetermined positional relationship relative to four reference points which are spaced from adjacent reference points by a first standard spacing and fall on auxiliary radial axes, wherein: said axiliary axes pass through said center point and intersect the main axes at an angle of 45*; the radially inner ends of said lateral side edges terminate at pairs of reference lInes parallel to and spaced by a second standard spacing from the auxiliary radial axes; the inner end of the one lateral side edge of each ridge is connected by an intersecting portion with that of the other lateral side edge of the adjacent ridge; one of the lateral side edges of each ridge extends along a line which diverges at an angle 3*-6* from an associated main radial axis and passes through an associated reference point; the other lateral side edge of said ridge extends along a line which converges toward the main axis at the same angle as said one lateral side edge and passes through a point nearer to the main axis than an associated reference point; and said intersecting portion is formed in a curved concave shape.
 2. A cross-recessed screw forming punching tool according to claim 1, wherein said intersection portion is shaped in the form of an arc having its center point equidistantly spaced from the inner ends of the lateral side edges of the adjacent ridges. 